Digital watermarking technique

ABSTRACT

A watermarking system allowing both sufficiently high quality of watermarked moving pictures and enhanced ease of watermark detection is disclosed. A watermark level of a watermark to be embedded into a picture of data is changed depending on the picture type of a selected block of frequency component data, and then a watermark having the watermark level is inserted into the selected block of frequency component data. Therefore, a moving-picture can be effectively embedded with a digital watermark without substantially reducing the quality of image and the digital watermark can be detected reliably. A relative proportion of watermark levels of I-picture, B-picture, and P-picture is preferably set to 10:7:5.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.09/642,476, filed 18 Aug. 2000, now U.S. Pat. No. 6,798,893, thecomplete disclosure of which is hereby incorporated by reference for allpurposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to digital watermarking of moving-picturedata and in particular to a method and system for inserting watermarkdata into the moving-picture data.

2. Description of the Prior Art

With wide-spreading digital satellite broadcasting, Internettransmission and DVD (Digital Video Disk), etc. in recent years, digitalimages are becoming easily accessible to users. Since the quality ofdigital images does not deteriorate when they are copied, securing theircopyrights has been an important issue.

For purposes of securing copyright protection for MPEG (moving pictureexperts group) data, there have been disclosed a watermarking system forembedding a plurality of watermarks into DCT (discrete cosine transform)coefficient domain of MPEG data and a watermark detecting system forextracting and detecting the embedded watermarks from the watermarkedMPEG data (see Japanese Patent Application Unexamined Publication No.11-55639).

More specifically, a plurality of watermarks different from each otherare previously stored each corresponding to picture types (I-, B-, andP-pictures in MPEG). In the watermarking system, one watermark isselected from the plurality of watermarks depending on the type of apicture to be encoded and is embedded into the image data in units of8×8 DCT coefficient block.

Assuming that f(1), f(2), . . . f(n) are DCT coefficients listed infrequency-ascending order, a watermarked coefficient F(i) is calculatedby the following equation:F(i)=f(i)+α×avg(f(i))×w(i),where i=1, 2, 3, . . . , n, w(i) is an element of a watermark selectedaccording to a normal distribution with mean mx=0 and variance σ²=1, αis a scaling element, and avg(f(i) )represents a local average overthree DCT coefficients in the neighborhood, which is calculated by thefollowing form:avg(f(i))=(|f(i−1)|+|f(i)|+|f(i+1)|)/3.

On the other hand, the watermark detecting system can detect an embeddedwatermark without the need of the original image data. The watermarkedMPEG data is decoded and a watermark is extracted from the DCTcomponents of the decoded data using the local average over theneighborhood. A watermark element W(i) is extracted by calculating thefollowing form: F(i)/avg(F(i)). A watermark element W(i) is accumulatedin one frame/field to produce WF(i).

A statistical similarity C between w(i) and WF(i) can be calculatedusing vector inner product as follows:C=WF×w/(|WF|×|w|),where WF=(WF(1), WF(2), . . . , WF(n)) and w=(w(1), w(2), . . . , w(n)).

If the statistical similarity C calculated as described above exceeds apredetermined threshold, it is determined that the correspondingwatermark is embedded in the MPEG data.

However, the inventor found that a degree of embedded watermark effecton MPEG data is varied depending on the type of a picture in MPEG. Ifwatermark frequency coefficients having a certain amplitude (level) isuniformly embedded to MPEG data regardless of the type of a picture asthe prior art, then there are cases where the quality of image isdeteriorated and the embedded watermark is hard to be detected.

More specifically, when the watermark is strongly embedded to the MPEGdata, ease of watermark detection is enhanced but the quality of imageis deteriorated. Contrarily, when the watermark is lightly embedded tothe MPEG data, the quality of image is kept sufficiently but theembedded watermark becomes hard to be detected. In other words, thequality of a watermarked image is traded off against watermark detectionefficiency.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a watermarkingsystem and method allowing both sufficiently high quality of watermarkedmoving pictures and enhanced ease of watermark detection.

According to the present invention, a method for inserting a watermarkinto a selected block of frequency component data in a picture of datahaving one of a plurality of picture types, includes the steps of:determining a picture type of the selected block of frequency componentdata; determining a watermark level depending on the picture type of theselected block of frequency component data; and inserting a watermarkhaving the watermark level into the selected block of frequencycomponent data.

The picture types are preferably Intra-frame coding picture (hereafter,I-picture), Inter-frame Predictive coding picture (hereafter, P-picture)and Bidirectionally Predictive coding picture (hereafter, B-picture),wherein a relative proportion of watermark levels of I-picture,B-picture, and P-picture is 10:7:5.

As described above, a watermark level of a watermark to be embedded intoa picture of data is changed depending on the picture type of a selectedblock of frequency component data, and then a watermark having thewatermark level is inserted into the selected block of frequencycomponent data. Therefore, a moving-picture can be effectively embeddedwith a digital watermark without substantially reducing the quality ofimage and the digital watermark can be detected reliably.

According to an embodiment of the present invention, a method includesthe steps of: storing a plurality of watermarks for each picture type,each of the watermarks corresponding to a different block of the pictureof data; determining a picture type of the selected block of frequencycomponent data; determining a watermark level depending on the picturetype of the selected block of frequency component data; selecting awatermark from the plurality of watermarks depending on which block isselected; and inserting a selected watermark having the watermark levelinto the selected block of frequency component data.

According to another embodiment of the present invention, a methodincludes the steps of: a) storing a plurality of watermarks for each ofthe picture types, wherein a watermark level of the watermarks variesdepending on a picture type; b) selecting a watermark of a typedepending on a picture type of the selected block of frequency componentdata; and c) inserting a watermark of a selected type into the selectedblock of frequency component data.

According to still another embodiment of the present invention, a methodincludes the steps of: a) storing a reference watermark; b) determininga picture type of the selected block of frequency component data; c)changing a watermark level of the reference watermark depending on thepicture type of the selected block of frequency component data toproduce a watermark to be used; and d) inserting the watermark to beused into the selected block of frequency component data.

In the step (c), the watermark level of the reference watermark may bechanged depending on both the picture type of the selected block offrequency component data and the selected block.

According to another aspect of the present invention, a method fordetecting a watermark from a selected block of frequency component datain a picture of data having one of a plurality of picture types,includes the steps of: storing a plurality of watermarks for each of thepicture types, wherein a watermark level of the watermarks variesdepending on a picture type; extracting a watermark from the selectedblock in the picture of data; selecting a watermark of a type dependingon a picture type of the selected block; and determining whether thestored watermark is embedded in the selected block, based on anextracted watermark with a selected watermark.

According to the present invention, a system for inserting a watermarkinto a selected block of frequency component data in a picture of datahaving one of a plurality of picture types, includes: a table storing aplurality of watermarks for each of the picture types, wherein awatermark level of the watermarks varies depending on a picture type; aselector for selecting a watermark of a type depending on a picture typeof the selected block of frequency component data; and an insertingsection for inserting a selected watermark of a selected type into theselected block of frequency component data.

According to the present inventions a system includes: a memory storinga reference watermark; a determiner for determining a picture type ofthe selected block of frequency component data; a multiplier formultiplying a watermark level of the reference watermark by a factorvarying depending on the picture type of the selected block of frequencycomponent data to produce a watermark to be used; and an insertingsection for inserting the watermark to be used into the selected blockof frequency component data.

The multiplier may multiply a watermark level of the reference watermarkby a factor varying depending on both the picture type of the selectedblock of frequency component data and the selected block.

The picture types are preferably Intra-frame coding picture (hereafter,I-picture), Inter-frame Predictive coding picture (hereafter, P-picture)and Bidirectionally Predictive coding picture (hereafter, B-picture),wherein a relative proportion of factors corresponding to I-picture,B-picture, and P-picture is 10:7:5.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a watermarkinsertion system according to a first embodiment of the presentinvention;

FIG. 2 is a block diagram showing a configuration of a watermarkdetection system according to the first embodiment of the presentinvention;

FIG. 3 illustrates a layered structure of an MPEG standard format;

FIG. 4 is a schematic diagram showing forward/backward predictionoperations in the MPEG standard format;

FIG. 5 illustrates a zigzag-scanning sequence;

FIG. 6 is a schematic diagram showing an example of watermark insertionoperation according to the present invention; and

FIG. 7 is a block diagram showing a configuration of a watermarkinsertion system according to a second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the preferred embodiments of the present invention will bedescribed in detail.

First Embodimemt

Referring to FIG. 1, an original image 101 stored in a frame/fieldmemory is divided into a plurality of k×k pixel blocks (here, k=8),which are sequentially read out as block image data 102. The block imagedata 102 is converted into DCT coefficient data by a DCT section 103 andthen the DCT coefficient data is quantized by a quantization section 104depending to a picture type of the original image 101. The quantized DCTcoefficient data is output to a watermark insertion section 105.

A picture type decision section 106 detects the picture type X of blockimage data 102 when the block image data 102 is encoded in a wayconforming to a predetermined standard such as MPEG or H.261. In MPEG2standard, each frame is one of three types of picture, Intra-framecoding Picture (hereinafter referred to as “I picture”), inter-framePredictive coding Picture (hereinafter referred to as “P picture”) andBidirectionally predictive coding Picture (hereinafter referred to as “Bpicture”).

The watermark insertion section 105 embeds a watermark selected by awatermark selector 107 to the quantized DCT coefficient data. Thewatermark selector 107 selects a watermark from a watermark table 108depending on the block location information and the picture type Xdetected by the picture type decision section 106.

The watermark table 108 contains three kinds of watermark, W(I), W(B),and W(P), corresponding to I-picture, B-picture, and P-picturerespectively. The I-picture watermark W(I) consists of N watermarks:W₁(I), W₂(I), . . . , W_(N)(I), which correspond to the blocks of anI-picture, respectively. The B-picture watermark W(B) consists of Nwatermarks: W₁(B), W₂(B), . . . , W_(N)(B), which correspond to theblocks of a B-picture, respectively. The P-picture watermark W(P)consists of N watermarks: W₁(P), W₂(P), . . . , W_(N)(P), whichcorrespond to the blocks of a P-picture, respectively. A watermark isrepresented by a set of watermark DCT coefficients.

According to the present embodiment, the relative proportion of therespective levels of I-, B-, and P-picture watermarks is set to|W(I)|:|W(B)|:|W(P)|=10:7:5. A set of watermark DCT coefficients,W_(j)(X) (j=1, 2, . . . , or N and X=I, B, or P), is obtained bymultiplying a reference watermark W(e) by a picture-dependent levelcoefficient k_(j)(X), that is, W_(j)(X)=k_(j)(X)×W(e), whereink_(j)(I):k_(j)(B):k_(j)(P)=10:7:5.

For example, the reference watermark W(e) may be 8-bit data “10101010”,in which the first bit represents the presence/absence of copyrightprotection, the second bit represents permission/inhibition of copying,and the third bit represents the limited number of copying operations.

Thereafter, the watermark-embedded DCT coefficient data isinverse-quantized by an inverse-quantization section 109 and then theoutput of the inverse-quantization section 109 is converted by aninverse-DCT (IDCT) section 110 into watermarked block image data 112,which is stored at the same location as the block 102 of the originalimage 101. By repeatedly performing the above procedure on the blocksover an entire frame/field of the original image 101, a watermarkedimage 111 is completed.

On the other hand, the watermark-embedded DCT coefficient data issubjected to Huffman-coding by an encoder 113 and the Huffman-coding isrepeatedly performed over the entire frame/field to produce compressedmoving-picture data 114 such as MPEG data. The compressed moving-picturedata 114 may be stored in a recording medium such as DVD or anotherstorage device.

Referring to FIG. 2, watermarked compressed data 201 that was producedas described above is decoded by a decoder 202 to producewatermark-embedded DCT coefficient data. The watermark-embedded DCTcoefficient data is inverse-quantized by an inverse-quantization section203 and then the output of the inverse-quantization section 203 isconverted by an IDCT section 204 into watermarked image data 205.

The watermark-embedded DCT coefficient data decoded by the decoder 202is also output to a watermark extractor 206. The watermark extractor 206extracts watermark data on a block-by-block basis from thewatermark-embedded DCT coefficient data and stores all the extractedwatermark data of a picture in a memory 207. Thereafter, a watermarkdetector 208 reads out the extracted watermark data on a block-by-blockbasis from the memory 207 and calculates a statistical similarity Cbased on the extracted watermark and a registered watermark selected bya watermark selector 209. As described before, by comparing thecalculated statistical similarity C with a predetermined threshold, itis determined whether the registered watermark is embedded in the blockin question.

The watermark selector 209 selects watermark data from a watermark table210 depending on the block location information and the type X of thepicture. The watermark table 210 contains the same contents as thewatermark table 108. That is, the watermark table 210 contains threekinds of watermark: W(I), W(B), and W(P) corresponding to I-picture,B-picture, and P-picture, respectively. Each of the I-, B-, andP-picture watermarks W(I), W(B), and W(P) consists of N watermarks, thatis, (W₁(I), W₂(I), . . . , W_(N)(I)), (W₁(B), W₂(B), . . . , W_(N)(B)),and (W₁(P), W₂(P), . . . , W_(N)(P)).

Operation

Hereafter, an operation of the present invention will be described,taking an example compressed moving-picture data conforming to MPEGstandard.

Referring to FIG. 3, image data that has been compressed according toMPEG standard has such a structure that a sequence header code SHC isfollowed by a sequence of GOP (group of picture). Here, data of eachframe/field of an image is written in a picture layer following apicture start code (PSC). Each frame or field is encoded in one of threetypes of picture format, I picture, P picture, and B picture.

As shown in FIG. 4, in the case of P picture and B picture, only adifference between the own picture and a reference picture at adifferent time instant is encoded as image data. Moreover, each pictureis subdivided into blocks and each block is subjected to the discretecosine transform (DCT). Then, the DCT coefficients are quantized with anappropriate quantizing coefficient and the quantized DCT coefficientsare subjected to two-dimensional Huffman coding.

The field data of each frame is inside a macro block (MB) layer under aslice layer following a slice start code (SSC). In the case where acolor difference format is 4:2:0, the field data of each frame isexpressed by a total of 6 block layers, 4 block layers indicatingbrightness data Y and 2 block layers indicating color difference data Cband Cr.

As shown in FIG. 5, in the case of zigzag scanning, quantized DCTcoefficients are scanned in a sequence of numbers and are converted to aone-dimensional sequence of 64 DCT coefficients. The position labeledwith “1” in the figure expresses a DC component of the DCT domain.Horizontal spacial frequency increases from this position “1” rightwardand vertical frequency increases from this position “1” downward. Thus,zigzag scanning virtually results in a one-dimensional sequence in orderfrom low-frequency components to high-frequency components. A watermarkis embedded to a block of MPEG data by adding each of watermark DCTcoefficients to a corresponding one of the 64 DCT coefficients.

Referring to FIG. 6, in the case where an original image is an I-pictureand a j-th block is read out, the watermark selector 107 selects theI-picture watermark W_(j)(I) from the watermark table 108. The watermarkinsertion section 105 adds the DCT coefficients of the selectedwatermark W_(j)(I) to corresponding ones of the quantized DCTcoefficients to produce a watermarked I-picture indicated by I+W(I).Similarly, in the case where an original image is a B-picture, thewatermark selector 107 selects the B-picture watermark DCT coefficientsW_(j)(B) from the watermark table 108.

The watermark insertion section 105 adds the selected watermark DCTcoefficients W_(j)(B) to corresponding ones of the quantized DCTcoefficients to produce a watermarked I-picture indicated by B+W(B). Inthe case where an original image is a P-picture, a watermarked P-pictureindicated by P+W(P) is produced by the watermark insertion section 105.

As described before, the relative proportion of the respective levels ofI-, B-, and P-picture watermarks is not equal. In this embodiment,|W(I)|:|W(B)|:|W(P)| is set to 10:7:5. Watermark DCT coefficientsW_(j)(X)(j=1, 2, . . . , N and X=I, B, or P) is obtained by multiplyingreference watermark data W(e) by a picture-dependent level coefficientk_(j)(X), that is, W_(j)(X)=k_(j)(X)×W(e), whereink_(j)(I):k_(j)(B):k_(j)(P)=10:7:5.

By setting the relative level proportion of the watermarks W(I), W(B)and W(P) to 10:7:5, picture degradation can be kept at a minimum whilethe watermark detection efficiency is kept at a sufficient level.

Further, the Inventor found that the larger the total of the relativelevel proportion values, I+B+P, (here, 1+0.7+0.5=2.2), the greaterpicture degradation. Relative to I+B+P=2.2, picture degradation becomesgreater in the case of I+B+P=3. Contrarily, in the case of I+B+P=1.5,picture degradation becomes smaller but an embedded watermark is harderto be detected.

Second Embodiment

A watermarking system according to a second embodiment of the presentinvention will be described with reference to FIG. 7, where circuitblocks similar to those previously described with reference to FIG. 1are denoted by the same reference numerals and the details will beomitted.

Referring to FIG. 7, the watermarking system according to the secondembodiment is formed by replacing a combination of the watermarkselector 107 and the watermark table 108 in the first embodiment with acircuit composed of a memory 301 storing a reference watermark W(e), Nmultipliers 302, N memories 303, and a watermark selector 304.

The respective watermarks W_(j)(X) (j=1, 2, . . . , N and X=I, B, or P),are obtained by the multipliers 302 multiplying the reference watermarkW(e) by N picture-dependent level coefficients k_(j)(X), that isW_(j)(X)=k_(j)(X)×W(e). More specifically, in the case of I-picture, therespective multipliers 302 are set at k₁(I), k₂(I), . . . , andk_(N)(I). Therefore, I-picture watermarks W_(j)(I) are obtained byk_(j)(I)×W(e). Similarly, in the case of B-picture, the respectivemultipliers 302 are set at k₁(B), k₂(B), . . . , and k_(N)(B), and inthe case of P-picture, the respective multipliers 302 are set at k₁(P),k₂(P), . . . , and k_(N)(P). Therefore, the watermark selector 304 canselect one of the watermarks stored in the memories 303 depending on thelocation of a block to be embedded with a selected watermark. This isthe same operation as the first embodiment.

As in the first embodiment, k_(j)(I):k_(j)(B):k_(j)(P) is preferably setto 10:7:5. Therefore, the same advantages as the first embodiment arealso achieved in the second embodiment. Further, according to the secondembodiment, only N memories 303 are needed to store the necessarywatermarks. Therefore, compared with the first embodiment, the necessaryamount of memory can be reduced.

The watermark selector 209 and the watermark table 210 in the watermarkdetection system as shown in FIG. 2 may be replaced with the circuitcomposed of the memory 301 storing the reference watermark W(e), the Nmultipliers 302, the N memories 303, and the watermark selector 304.

The above-described embodiments have been explained taking the MPEGstandard coding system as an example, but of course the presentinvention is applicable to other image coding systems using DCT, forexample, JPEG standard and H.261 as well.

The watermark insertion and detection according to the above describedembodiments can also be implemented by a computer running a program thatinstructs the computer to execute these operations.

As described above, according to the present invention, the amplitude orlevel of a watermark to be embedded to moving-picture data is set to anoptimal level for each picture type in the moving-picture data.Therefore, both sufficiently high quality of watermarked moving picturedata and enhanced ease of watermark detection can be achieved.

1. A method for inserting a watermark into a selected block of frequencycomponent data in a picture of data having one of a plurality of picturetypes selected from the group comprising I-picture, B-picture, andP-picture types, the method comprising the steps of: determining apicture type of the selected block of frequency component data;determining a watermark level depending on the picture type of theselected block of frequency component data; and inserting a watermarkselected from a plurality of watermarks stored in a table having thewatermark level into the selected block of frequency component data,wherein a total of relative proportion values of watermark levels ofI-picture, B-picture, and P-picture types is equal to or smaller thanthree times a normalized watermark level of an I-picture type.
 2. Amethod for inserting a watermark into a selected block of frequencycomponent data in a picture of data having one of a plurality of picturetypes selected from the group comprising I-picture, B-picture, andP-picture types, the method comprising the steps of: storing in a tablea plurality of watermarks for each picture type, each of the watermarkscorresponding to a different block of the picture of data; determining apicture type of the selected block of frequency component data;determining a watermark level depending on the picture type of theselected block of frequency component data; selecting a watermark fromthe plurality of watermarks depending on which block is selected; andinserting a selected watermark having the watermark level into theselected block of frequency component data, wherein a total of relativeproportion values of watermark levels of I-picture, B-picture, andP-picture types is equal to or smaller than three times a normalizedwatermark level of an I-picture type.
 3. A method for inserting awatermark into a selected block of frequency component data in a pictureof data having one of a plurality of picture types selected from thegroup comprising I-picture, B-picture, and P-picture types, the methodcomprising the steps of: a) storing in a table a plurality of watermarksfor each of the picture types, wherein a watermark level of thewatermarks varies depending on a picture type; b) selecting a watermarkof a type depending on a picture type of the selected block of frequencycomponent data; and c) inserting a watermark of a selected type into theselected block of frequency component data, wherein a total of relativeproportion values of watermark levels of I-picture, B-picture, andP-picture types is equal to or smaller than three times a normalizedwatermark level of an I-picture type.
 4. A system for inserting awatermark into a selected block of frequency component data in a pictureof data having one of a plurality of picture types selected from thegroup comprising I-picture, B-picture, and P-picture types, the systemcomprising: a table storing a plurality of watermarks for each of thepicture types, wherein a watermark level of the watermarks variesdepending on a picture type; a selector for selecting a watermark of atype depending on a picture type of the selected block of frequencycomponent data; and an inserting section for inserting a selectedwatermark of a selected type into the selected block of frequencycomponent data, wherein a total of relative proportion values ofwatermark levels of I-picture, B-picture, and P-picture types is equalto or smaller than three times a normalized watermark level of anI-picture type.
 5. A method for detecting a watermark from a selectedblock of frequency component data in a picture of data having one of aplurality of picture types selected from the group comprising I-picture,B-picture, and P-picture types, comprising the steps of: storing aplurality of watermarks for each of the picture types, wherein awatermark level of the watermarks varies depending on a picture type anda total of relative proportion values of watermark levels of I-picture,B-picture, and P-picture types is equal to or smaller than three times anormalized watermark level of an I-picture type; extracting a watermarkfrom the selected block the picture of data; selecting a watermark fromthe stored plurality of watermarks depending on a picture type of theselected block; and determining whether the selected watermark isembedded in the selected block, based on the extracted watermark and theselected watermark.
 6. A digital watermarking method comprising thesteps of: at a watermark inserting section for inserting a watermarkinto a selected block of frequency component data in a picture of datahaving one of a plurality of picture types selected from the groupcomprising I-picture, B-picture, and P-picture types, storing aplurality of watermarks for each picture type, each of the watermarkscorresponding to a different block of the picture of data; determining apicture type of the selected block of frequency component data;determining a watermark level depending on the picture type of theselected block of frequency component data; selecting a watermark fromthe plurality of watermarks depending on which block is selected; andinserting a selected watermark having the level into the selected blockof frequency component watermark data, wherein a total of relativeproportion values of watermark levels of I-picture, B-picture, andP-picture types is equal to or smaller than three times a normalizedwatermark level of an I-picture type, and at watermark detecting sectionfor detecting a watermark from a selected block of frequency componentdata in a picture of data having one of a plurality of picture types,storing a plurality of watermarks for each of the picture types, whereina watermark level of the watermarks varies depending on a picture typeand a total of relative proportion values of watermark levels ofI-picture, B-picture, and P-picture types is equal to or smaller thanthree times a normalized watermark level of an I-picture type;extracting a watermark from the selected block in the picture of data;selecting a watermark from the stored plurality of watermarks dependingon a picture type of the selected block; and determining whether theselected watermark is embedded in the selected block, based on theextracted watermark and the selected watermark.
 7. A digitalwatermarking system comprising: a watermark inserting device forinserting a into a selected block of frequency component data in of datahaving one of a plurality of picture types selected from the groupcomprising I-picture, B-picture, and P-picture types; and a watermarkdetecting device for detecting a from a selected block of frequencycomponent data in of data having one of a plurality of picture types,wherein the watermark inserting device comprises: a first table storinga plurality of watermarks for each of the picture types, wherein awatermark level of the watermarks varies depending on a picture type; afirst selector for selecting a watermark of a type depending on apicture type of the selected block of frequency component data; and aninserting section for inserting a selected watermark of a selected typeinto the selected block of frequency component data, wherein a total ofrelative proportion values of watermark levels of I-picture, B-picture,and P-picture types is equal to or smaller than three times a normalizedwatermark level of an I-picture type, and the watermark detecting devicecomprises: a second table for storing the plurality of watermarks foreach of the picture types, wherein a watermark level of the watermarksvaries depending on a picture type and a total of relative proportionvalues of watermark levels of I-picture, B-picture, and P-picture typesis equal to or smaller than three times a normalized watermark level ofan I-picture type; an extractor for extracting a watermark from theselected block in the picture of data; a second selector for selecting awatermark from the stored plurality of watermarks depending on a picturetype of the selected block; and a determiner for determining whether theselected watermark is embedded in the selected block, based on theextracted watermark and the selected watermark.